1. School of Information Engineering, Inner Mongolia University of Science and Technology, Baotou 014010, China
2. State Key Laboratory of Network and Switching Technology, Beijing University of Posts and Telecommunications, Beijing 100876, China
3. Department of Computer, Tianjin Ren’ai College, Tianjin 301636, China
4. College of Information, North China University of Technology, Beijing 100144, China
5. Department of Computer Science and Mathematics, Sul Ross State University, Alpine, TX 79830, USA